Expression of the 75 kDA TNF receptor and its role in contact-mediated neuronal cell death

We previously demonstrated TNF toxicity, at high TNF doses or in the presence of actinomycin D, in the N1E-115 neuronal cell line (N1Es), which expresses only the 55 kDa TNF receptor (TNFR). To determine whether presence of the 75 kDa TNFR increases N1E sensitivity to TNF toxicity, cells were transfected with a 75 kDa TNFR expression construct. However, 75 kDa TNFR protein expression was undetectable in stably transfected N1Es. Further investigation revealed endogenous membrane-associated TNF in this neuronal line. Co-transfection with beta-galactosidase and the 75 kDa TNFR or empty vector (pcDNA3) indicated cell loss in the 75 kDa TNFR-transfected population relative to vector-transfected populations, while inhibition of membrane-associated TNF with a neutralizing antibody led to increased 75 kDa TNFR expression in transiently transfected N1Es. We conclude that neutralization of membrane-associated TNF inhibits its interaction with the introduced 75 kDa TNFR, increasing neuronal survival and promoting 75 kDa TNFR expression. Induced 75 kDa TNFR expression in the presence of membrane-associated TNF and the 55 kDa TNFR results in lymphocyte cell death [J.K. Lazdins, M. Grell, M.R. Walker, K. Woods-Cook, P. Scheurich, K. Pfizenmaier, Membrane tumor necrosis factor (TNF) induced cooperative signaling of the TNFR60 and TNFR80 favors induction of cell death rather than virus production in HIV-infected T cells, J. Exp. Med. 185 (1997) 81-90]. This report demonstrates that membrane-associated TNF and the 75 kDa TNFR similarly contribute to neuronal cell death.